The present invention relates to the magnetic resonance (MR) art. It finds particular application in conjunction with an interventional radio frequency (RF) coil assembly for use in magnetic resonance guided neurosurgery, and will be described with particular reference thereto. However, it should be appreciated that the present invention may also find application in conjunction with other types of neurosurgical and diagnostic imaging systems.
When performing surgery on a patient's brain, the patient's head is usually held fixed by a head frame. Known head frames typically include a clamp or frame-like structure with several sharp pins that are anchored in the patient's skull in order to immobilize the frame-like structure relative to the patient's head. The head frame is connected to a surgical table by a series of links and joints that permit the head frame to be positioned with respect to the table with several degrees of freedom. By this means, the head frame can be positioned to hold the patient's head in a range of orientations to present the surgeon with an appropriate approach to the surgical field. However, access to the patient's head is still restricted by the head frame.
Conventional head frames include the designs of Ohio Medical (Cincinnati, Ohio.) and many other companies. The most common model is the Mayfield frame made by Ohio Medical and described in U.S. Pat. Nos. 4,169,478 and 5,269,034. The Mayfield frame is made from cast aluminum and is not MR compatible. In MR guided neurosurgery, the head frame must be made from an MR compatible material. Ohio Medical and Elekta Instruments (Atlanta, Ga.) both make radiolucent head frames for intraoperative x-ray or CT imaging. These products are made from a carbon fiber/epoxy composite and have been used for intraoperative MR imaging. An exemplary radiolucent head frame is described in U.S. Pat. No. 5,537,704.
When performing neurosurgery with MR guidance, a receive surface coil is used for local imaging of a patient's brain because a higher signal-to-noise ratio can be obtained than with a whole body RF coil. The surface coil is designed to be placed as close as possible to the patient's head to increase the signal to noise ratio. The surface coil is typically covered by a sterile bag or placed on the patient prior to applying sterile drapes. As with head frames, surface coils typically restrict access to the patient's head.
Research and development is presently being conducted on specific surface coil designs for use in MR guided neurosurgery. For horizontal field interventional MR, flexible surface coils, either of a single-solenoid or Helmholtz configuration are being contemplated. These coils would generally be used with the loops in the coronal plane, with a non-sterile loop below the patient's head and a sterile or sterile-bagged loop above the patient's head. For vertical field interventional MR, flexible single-solenoid surface coils are contemplated. These coils are oriented in the transverse plane, placed around the patient's head. The known surface coil designs are not easily sterilized.
Thus, in MR guided neurosurgery, both the head frame and the surface coil restrict access to the patient's head. Further, it is often difficult to position both the surface coil and the head frame so as to keep the region of interest in the sensitive volume of the surface coil and to allow sufficient access for surgery. If the surface coil has to be moved away from the anatomy of interest to allow space for the head frame or access for the surgeon, the signal to noise ratio will suffer.
The present invention contemplates a new and improved interventional radio frequency coil assembly for use in magnetic resonance guided neurosurgery that overcomes the above-referenced problems and others.